1. Field of the Invention
The present invention relates to automatic temperature regulators, particularly in boilers and other closed fluid heaters with flow controlled therein.
2. Description of the Prior Art
Oil-fired water heating systems are primarily installed to provide required heating of the space within a house by use of hot water-filled radiators. The installation of a water coil immersed in a heat exchange relationship with water being heated inside a storage tank provides a secondary function of heating water for domestic uses, such as bathing and cleaning.
Such a method of heating water for domestic uses is the least desirable from the standpoint of quality and efficiency but continues to be used in older houses because a large amount of capital is already invested in the oil-fired boiler. Such a boiler has a storage tank for supplying hot water to radiators for heating the entire space within the house. The quality of the hot water for domestic uses varies widely during usage due to large swings in temperature and, thus, is quite substandard. This poor quality occurs because, as implied above, the boiler control systems presently used in older house heaters are sensitive only to large changes in the temperature of the water in the boiler for space heating and not to changes in the temperature of the water in the heat exchanger for domestic uses.
The method of boiler control presently used in many house heaters provides three basic control points. First, there is a high shutoff point which limits the maximum water temperature to a safe value to avoid overpressurization of the boiler and so that scalding is avoided. Second, there is a normal high temperature shutdown point which normally stops the firing of the boiler when the water reaches an upper desired storage temperature. However, in many new control systems, the temperature of the water in the boiler is allowed to exceed this point whenever the boiler is supplying hot water for heating space in the house via the radiators. Nevertheless, the maximum temperature attainable still does not exceed the high limit shutoff point. Third, there is a low temperature start-up point which begins firing of the boiler at the lowest temperature at which water may be satisfactorily used for domestic purposes.
In all cases, boiler control by thermostats, such as capillary tubes for sensing temperature, even in the newest house heating systems, is nonresponsive to and grossly inadequate for the requirements of water usage for domestic purposes.
There are several reasons why the current burner controls are disadvantageous. First of all, the prior art controls require the temperature of all water inventoried in the boiler to fall to the low temperature start-up point before the tank thermostat commences firing of the burner. This arrangement means that the burner must heat up the entire inventory of water contained in the jacket in order to simply raise the temperature of the water being drawn through the heat exchanger for domestic use. Thus, such an arrangement unnecessarily delays the response of the burner and, consequently, results in wide temperature fluctuations and slow boiler recovery.
A second reason why the current burner controls are disadvantageous is that at least three different practices are used in an attempt to alleviate the problem of the boiler not maintaining the temperature of the water at a satisfactorily high degree during usage for domestic chores. Unfortunately, each of these three practices has a definitely counterproductive aspect.
The first of these practices is increasing the size of the boiler so that there is a larger amount of water in inventory at all times, thus ostensibly making more hot water available for a longer continuous period of time. However, the drawback to this practice is that more water is used for domestic purposes at a poor quality for a longer time before the tank thermostat turns on the burner. Ideally, the water in the boiler should represent a heat source in a heat exchange relationship with the water in the coil instead of the water in the boiler continuing unproductively as a heat sink for the energy produced by the burner.
The second practice with a counterproductive aspect is installing a burner which is greatly oversized in relation to the amount of water required for heating all space in the house. Although allowing the temperature of the water in the boiler to catch up more rapidly to the temperature of the water in the coil for domestic use once firing of the burner does start, this arrangement has the drawback that the energy input defined in units of costly fuel oil greatly exceeds the energy output required in terms of the heat needed to raise the temperature of the water in the coil for domestic usage.
The third practice with a counterproductive aspect is that the usual temperature of the water inventoried in the jacket is maintained above the temperature found satisfactory for most domestic end uses. Normally, water at the point of exiting a facuet for domestic use is tempered by mixing it with cold water. This arrangement has the disadvantage that automatic appliances, such as dishwashers and clothes washers, utilize untempered water at a higher than required temperature, at greater cost to the homeowner, before the water reaches the low temperature start-up point.
All three practices discussed immediately hereinabove have the effect of lowering the operating efficiency of the boiler in the following ways. First, increased exposure of the heated external jacket surfaces required to contain a larger reservoir of water causes greater heat losses to the area which houses the boiler. Second, overfiring of the burner reduces the seasonal efficiency of the boiler because, due to the nature of a combustion heating system, its best efficiency is at a steady-state condition. In other words, a greater overfiring rate with respect to the space heating requirements of a house causes a lower efficiency in the operation of the boiler. Third, maintenance of unnecessarily high water temperatures inside the jacket causes increased losses to the area which houses the boiler. Fourth, the maintenance of unnecessarily high jacket temperatures also increases the rate of scale formation in the boiler, thus further reducing the operating efficiency and life of the boiler. Fifth, if the temperature is sufficiently high, a safety risk arises because the accidental use of untempered water may pose a danger of scalding to users.
Various attempts have been made in recent years to overcome these problems and to conserve energy by using socalled instantaneous or anticipatory thermostats in oil-fired water heating systems. However, many of these thermostats are intended for use in heating systems to be installed in new houses or, if intended for use in heating systems already in older houses, are complicated and require installation by skilled workers. Exemplary water heating systems employing such prior art thermostats are disclosed in U.S. Pat. Nos. 4,501,261, 4,413,775, 4,371,779, 4,354,094, and 4,166,944. Unfortunately, none of the anticipatory thermostats disclosed in these references are simple enough that they can be installed by a homeowner at great savings in skilled labor and fuel costs.